Heating device



I :Iuhe 30, 1970 E. ANDRICH 0 I HEATING DEVICE Filed March 27. 1968 YINVENTOR. EKKEHARD ANDRICH BY w fl H 1 AGE United States Patent Oflice3,518,407 Patented June 30, 1970 3,518,407 HEATING DEVICE EkkehardAndrich, Aachen, Germany, assignor, by mesne assignments, to US. PhilipsCorporation, New York, N.Y., a corporation of Delaware Filed Mar. 27,1968, Ser. No. 716,424 Claims priority, applicatigai gzrmany, Apr. 4,1967,

Int. Cl. B23k 3/222; H05b 3/12 U.S. Cl. 219-229 4 Claims ABSTRACT OF THEDISCLOSURE The invention relates to a heating device adaptable for usewithin an electric soldering iron. In particular, this heating deviceutilizes a heating element having a resistance which jumps to a highvalue when a certain temperature is exceeded. The use of such materialswhich have a positive temperature coefficient is well known and commonlyreferred to as PTC resistance elements or cold conductors. A materialsuch as barium titanate, can be chosen so that when a temperature T isexceeded, the resistance value increases by a higher power of 10.

Known devices using PTC elements have a disadvantage in that theelectric current flows through a comparatively thick resistance elementand when heat is emitted, a non-homogeneous voltage drop occurs in thePTC resistance such that the voltage drop and the emission of heat takesplace mainly as remotely as possible from the heat-emitting surface.Consequently, the poor thermal conductivity of the PTC resistanceresults in a loss of heat. The heat developed inside the element is theninsufficiently supplied to the heat-emitting area due to the non-uniformheating and the non-uniform voltage jumps in the element.

This invention is characterized in that an electric supply current fiowsthrough a plate-shaped PTC resistance element in the direction of itsthickness, and the resistance element is arranged with respect to aheat-emitting area so that during the emission of heat a temperaturegradient occurs along the element (i.e. at right angles to the directionof the current). It should be noted that the development of heat is notthe same in the various parts of the element, and this is usedadvantageously.

The invention will now be described more fully with reference to theaccompanying drawing, in which:

FIG. 1 shows the heating part of a soldering iron.

FIG. 2 shows a modification of FIG. 1.

The device shown in FIG. 1 includes a resistance element 1 made of amaterial having a resistance which jumps to a high value when atemperature T is exceeded.

Preferably, a barium-lead titanate is used, the jumping temperature T ofwhich lies at approximately 340 C. The element 1 has the form of a thinplate having a thickness of, for example, 1 mm., the largest surface ofwhich is covered with a metal foil 2. and 3, respectively. (In thedrawing, these metal foils are spaced by a certain distance from theplate 1 for the sake of clarity, but in actual fact, they are locatedvery close to the plate 1.) Insulating mica foils 4 and 5, respectively,insulate the foil-s 2 and 3, respectively, from the wall 6 of thermallygood conducting material, for example, copper. The soldering tip isdenoted by 7 and also consists of a thermally good conducting material,for example, copper; it may be integral with the wall 6. The elements 1,2, 3, 4, 5, 6 are spaced apart in the drawing for the sake of clarity,but in actual fact they are located very close to each other.

The electric current is applied to the metal foils 2 and 3,respectively, and flows through the plate 1 and hence in the, directionof the arrow i at right angles to the greatest surface area of theplate 1. Thus, the element is heated and the heat is conducted to thewall 6 and the soldering tip 7. In the rest condition (i.e. without thesupply of soldering power), an operating temperature of the plate of,for example, 350 C. to 360 C. is adjusted, which exceeds the temperatureT This themperature prevails, throughout the plate and the current inthe plate is comparatively small.

During the soldering operation, the power is supplied mainly through thesoldering tip 7. As a result, a temperature gradient occurs along thewall 6 and the plate 1; the coldest area is located close to thesoldering tip 7 so that the current and the power produced in the plate1 are a maximum at this area.

The heat is emitted mainly in the direction of the point of the arrow W,i.e. at right angles to the direction of the current i. The temperatureof the resistance element 1 increases in a direction away from thesoldering tip 7 (i.e. in the direction of the righthand end of theresistance element 1). Thus, only a small current flows at this end ofthe resistance element 1 and the power produced does not increase much.If during operation of the soldering iron, a larger quantity of heat Wis derived,

the zone of low temperature is enlarged further (to the right) over theplate and the development of heat automatically matches the need ofheat.

In the device shown in FIG. 2, the soldering tip 7 is joined not only tothe wall 6 but also to a central plate .8, the wall and the plate bothconsisting of a thermally good conducting material. Between the centralplate 8 and the wall 6 are sandwiched several plate-shaped resistanceelements 1 (which are again provided on either side with metalcurrent-supply foils and are insulated from the wall 6 and from thecentral plate 8 by insulating foils. Also in this case, the zone of lowtemperature is enlarged with an increased emission of heat (direction W)over a larger distance from the soldering tip 7 (i.e. at right angles tothe direction 1' of the current through the resistance elements 1).

What is claimed is:

1. A heating device for use within a soldering iron and comprising aplate-shaped positive temperature coefficient resistance element, meansfor creating a current flow transversely across and through theresistance element, heat insulating means for permitting heat flow in adirection perpendicular to the current How, and heat emitting tip meansthermally coactive with the resistance element for producing alongitudinal temperature gradient lengthwise along the resistanceelement during-heat emission.

2. A heating device as claimed in claim 1 wherein the means for creatinga current flow includes sheets of metal foil placed parallel to and oneither side of the resistance element.

3. A heating device as claimed in claim 4 wherein sheets of insulatingmica foil are placed parallel to and on either side of the conductivemetal foil.

. 4 4. A heating device as claimed in claim 3 comprising a 1,609,920 12/1926 Whited 219-236 X centralplate of a thermal conducting materialextending 3,400,250 9/1968 Buiting et al.' 219-505 X from the tip means,and a plurality of resistance elements 3,414,705 12/ 1968 Marcoux 219210positioned on either side of the central plate. 3,414,706 12/1968Flanagan et a1 219210 References Cited 5 ANTHONY BARTIS, PrimaryExaminer UNITED STATES PATENTS s L R6.236,619 2/1953 Weller 219 235 219241 ,05. 22 51 1,363,473 12/1920 Kuhn et a1 219-238 X

